Reinforcing rod

ABSTRACT

A reinforcing rod made from fiber-reinforced plastic is provided on its peripheral surface with profiling projecting outwardly in the radial direction in the form of ribs extending at least across one part of the periphery. The reinforcing rod has ribs with different geometric and/or material properties.

The invention relates to a reinforcing rod made from fiber-reinforcedplastic that is provided on its peripheral surface with profilingprojecting outwardly in the radial direction in the form of ribsextending at least across one part of the periphery.

From DE-A-101 21 021, such a reinforcing rod made from fiber-reinforcedplastic is known, which starts with the problem of providing aload-bearing bond with the concrete surrounding the plastic reinforcingrod. Here, in particular, two types of failures, which are to beavoided, come into question: first, the shearing of the ribs as aconsequence of axial tensile loads that are too high and insufficienttransmission of the effective forces from the concrete into thereinforcing rod and vice versa; second, the risk of the so-calledsplitting tensile failure in ribs that are too flat, through which, fortensile loads, the concrete surrounding the ribbed reinforcing rod isexposed to a rod circumference that becomes increasingly bigger and theconcrete finally bursts open. In DE-A-101 21 021, it is proposedaccordingly that the side flanks of the ribs of the reinforcing rodshould be arranged inclined at an angle of more than 45° relative to therod axis and that the axial width of the ribs should be greater than thedistance between two adjacent ribs.

In this way it should be guaranteed that bursting open of the concretedue to angles of the rib flanks that are too flat is prevented and,above all, that the ribs have an adequate bond with the rest of thereinforcing rod.

This second aspect of the improved bond has been attempted to berealized in other known reinforcing rods such that the rod surface isprovided with sanding, thread-shaped windings (see, e.g., EP-A-0 199348) or twisted sections (or narrowed sections). A common measure,however, consists in cutting trapezoidal threads, which similarlyproduces ribs—or rather one single thread-shaped, peripheral, continuousrib—in the rod region left between the recesses of adjacent threads.

Accordingly, the following refers to ribs not only when these projectoutwardly starting from an inner casing surface with smaller diameter,but also when these—as in the case of notched threads—are made from apart of the rod casing surface and are constructed by recesses machinedinto this casing surface.

For a known embodiment, a thread geometry is defined, in which theconcrete corbels, that is, the concrete located adjacent to the rod inthe region between two adjacent ribs, fail up to a certain strength ofthe concrete between the ribs. A disadvantage in this thread shape isthat for a higher concrete strength, the ribs shear off completely andthe remaining bond strength falls drastically. Because concretecontinuously stiffens with increasing aging, this can also lead toabrupt failure of the reinforcement when a threshold is exceeded evenafter a long, undamaged time.

Typically, in concrete constructions it is attempted to limit crackwidths for not only visual, but also mechanical reasons. Becausereinforcing rods made from fiber-reinforced plastic (so-called GFKreinforcing rods) have a lower modulus of elasticity than steel andtherefore wider cracks are to be expected in GFK-reinforced concreteconstructions compared with steel concrete constructions with the samereinforcement content, currently reinforcing rods made from steel arealso still used.

SUMMARY

Starting with these conditions, the present invention is based on theobjective of making available a reinforcing rod made fromfiber-reinforced plastic of the type noted above, which distinguishesitself through improved properties and which is suitable, in particular,for receiving higher loads. In particular, a reinforcing rod made fromfiber-reinforced plastic shall be provided, which avoids thedisadvantage of conventional GFK reinforcing rods and in this way helpsreduce, for example, the crack spacing and the crack width in theconcrete surrounding the reinforcing rod. In this way, advantageouslyinstead of a few large gaping cracks in the concrete, preferably severalsmaller cracks should be produced, which then create, in addition to abetter visual impression, also improved ductility of the concretecomponent.

This objective is met according to the invention in such a way that thereinforcing rod has ribs with different geometric and/or materialproperties. In this way, an order system for different rib propertiescan be formed, in which the ribs of different orders can bedistinguished with respect to geometric parameters such as rib width,rib spacing, rib depth, angle of the rib flanks, rib pitch, etc., or byvariation of the fiberglass content, the fiber materials, the fiberorientations, etc., and can supplement their properties.

Advantageous improvements of the reinforcing rod according to theinvention are the subject matter of the dependent claims, whose wordingis incorporated into the description by reference, in order to avoidunnecessary repetition of the text.

Advantageously, the ribs are constructed with different geometric and/ormaterial properties in such a way that they have a different shear loadon the rib base. In this way, the mentioned order system of differentrib properties advantageously leads to a differentiation with respect tothe rib load-bearing capacities.

The properties of ribs of higher order are preferably selected so thatthe shear load on the rib base of ribs of higher order is greater thanthe shear load on the rib base of ribs of lower order.

Above all it should be guaranteed that the ribs are constructed withdifferent geometric and/or material properties in such a way that, inthe load case, they do not fail at the same time and/or under the sameload, as is the case, for example, in known reinforcing rods from thestate of the art (see, e.g., WO 95/13414) with two thread-shaped,opposite-sense, crossing ribs, which are arranged symmetric in the axialdirection. This configuration means symmetric shear loading and thususually simultaneous failure. If failure at the same point in timeand/or under the same load can be prevented, this increases theductility of the reinforcing rod.

So that the ribs can be mutually supported or supplemented withdifferent rib geometries and/or rib materials using means and methodsaccording to the invention, they should be arranged at least inapproximately the same axial section of the reinforcing rod—eitherbordering adjacent to each other in the axial direction or spaced apartfrom each other or mutually overlapping or superimposed.

In this way, for example, a special advantage is given in that one cancombine wide ribs of a first order with narrower ribs of a second orhigher order in such a way that the narrower ribs are arranged on thewider ribs on their radial outer side. In this way it can be achievedthat in the load case, initially the narrower ribs of second order aresheared off when the stress on the rib bases of these narrower ribsexceeds their shear strength.

By shearing off these narrower ribs, the contact surface of thereinforcing rod in the region of the remaining wider ribs of first orderwith the concrete corbel surrounding the reinforcing rod is reduced andthus the load on the rib base of these wider ribs of first order isinitially reduced. Thus, the remaining ribs of first order can receiveadditional loads again until the shear stress also exceeds the shearstrength on the rib base of the ribs of first order and leads to theirbeing sheared off.

With the help of the different rib properties, an “onion peel effect” isessentially produced: certain loads initially lead to damage to the“outer onion peel,” i.e., the narrower or outer ribs of higher order.These sheared ribs no longer contribute to the reinforcing rod beingable to receive tensile stress in the concrete, but instead lie looselybetween the reinforcing rod and concrete, wherein the stress is receivedby the remaining ribs (of lower order). If the load increases, then,when the associated threshold is exceeded, this leads to a failure ofthe ribs of the next lower order, etc. Finally, despite damaged, stillpresent, loose “outer onion peels,” i.e., ribs of higher order, the bondof the concrete with the “innermost onion peel,” i.e., the ribs of firstorder still remains.

For this “onion peel effect,” what is important is primarily thatdespite any possible sheared-off ribs of higher order, the remainingload-bearing capacity of the rib(s) of lower order has a defined value,which then provides further load-bearing capacity to the associatedreinforcing rod.

The ribs of different order can be arranged not only synchronously, forexample, rotationally symmetric, thread-shaped, or running in oppositesenses uniformly across the reinforcing rod, but instead they can alsofollow different arrangement patterns, for example, with opposite,different slopes up to a point-shaped distribution of the ribs ofhighest order, which can be formed, for example, by sanding (forpositive ribs) or sandblasting (for negative ribs), which has theadvantage of higher bond activation for small slip paths. In this way,however, defined properties in the sanded or sandblasted regions shouldbe observed, in order to prevent undefined randomness and thus negativeeffects in the loaded state.

Due to the order system of various rib properties according to theinvention, when certain load thresholds are exceeded, sudden shearingoff of all of the ribs and failure of the entire reinforcement providedby the reinforcing rod does not take place—which is different from rodsof the state of the art. Instead, at first only the ribs of highestorder that can be loaded least shear off. In this way, the remainingcontact surface of the reinforcing rod with the concrete corbelsdecreases, the slip between the rod and concrete increases, and leads,according to the invention, to very advantageous load-bearing reserves.

Only when the load increases—for example, when the concrete strengthincreases over time—do the ribs with the next lower order shear off whenthe corresponding threshold is exceeded.

It should be noted that in the state of the art of the steel reinforcingrods, there are already structural shapes, which are aimed at a “steppedfailure mode” with the goal of avoiding too much deformation of thesteel and of keeping its ductility high. Here, the rod material in theregion of the ribs should not fail—as in the present plastic reinforcingrods—but instead the concrete surrounding the rod fails in the region ofan individual concrete corbel, before, in a next step, the concretefails in the region of a larger concrete corbel. While a primary goal inthe present invention is to provide a defined residual load-bearingcapacity, in this state of the art, due to the stepped failure mode,larger relative displacements of the steel rod relative to the steelconcrete component reinforced in this way are desired and allowed, sothat the steel concrete component can also be dimensioned under use oflocal plastic deformation of the reinforcement.

Thus, in addition, rib geometry for a high-load rib can be provided,which can also be used for concrete with the highest strength and doesnot lead to rib failure of the reinforcement, but instead at most to afailure of the concrete corbel between the ribs. While ribs with lowerstrength guarantee a good bond in normal concrete, the high-strengthribs provide a minimum bond strength also for greatly aftercuredconcrete or overstrength concrete.

Finally, ribs of different order can be combined in a multiple step rib,which can feature discrete angle jumps or continuous changes in angle.In this way, different rib properties are combined with each other,wherein, in turn, the ribs of higher order have a lower shear strengthand fail earlier than the ribs of lower order. In this way it can beprevented that the entire rib shears off at a certain point in time;instead initially one of the fractional sub-ribs shears off, because thestress in the rib base of this sub-rib exceeds the shear strength.Therefore, the contact surface of the remaining sub-ribs with theconcrete surrounding them, the so-called concrete corbel, is reduced andthus the load on the rib base of these remaining sub-ribs is reduced.Thus, these remaining sub-ribs can again receive additional loadinguntil the shear stress on the rib base of then the smallest sub-rib isexceeded and leads to its shearing.

For the production of such a reinforcing rod according to the invention,in addition to the conventional method (such as, e.g., shaping of theribs during the pultrusion process), milling of the rib geometry inhardened reinforcing rods is also possible, by means of which withoutgreat expense many different geometric properties can be achieved. Inthis way, the basic profile of the reinforcing rod can also have anoval, rectangular, star-shaped, etc. cross section that is differentfrom a circular shape. Likewise, the milling process can be a circularor oval, central or eccentric process. By combining the basic profile ofthe reinforcing rod and milling process, with very simple meansdifferent geometric properties can be achieved and thus various ribstrengths can be represented.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Additional features and advantages of the present invention emerge fromthe following description of various embodiments with reference to thedrawing; shown herein are:

FIGS. 1 a)-1 g) show a first embodiment of a reinforcing rod accordingto the invention

in side view—in FIG. 1 a),

in vertical section—in FIG. 1 b),

in horizontal section along A-A from FIG. 1 a)—in FIG. 1 c),

in horizontal section along B-B from FIG. 1 a)—in FIG. 1 d),

the detail A from FIG. 1 b)—in FIG. 1 e),

the detail B from FIG. 1 b)—in FIG. 1 f), and

in perspective side view—in FIG. 1 g);

FIGS. 2 a) and 2 b) show a second embodiment of a reinforcing rodaccording to the invention in side view—in FIG. 2 a)—and in perspectiveside view—in FIG. 2 b);

FIGS. 3 a) and 3 b) show a third embodiment of a reinforcing rodaccording to the invention in side view—in FIG. 3 a)—and in perspectiveside view—in FIG. 3 b);

FIG. 4 is a partial vertical section view through a fourth embodiment ofa reinforcing rod according to the invention;

FIG. 5 is a partial vertical section view through a fifth embodiment ofa reinforcing rod according to the invention;

FIG. 6 is a partial vertical section view through a sixth embodiment ofa reinforcing rod according to the invention; and

FIG. 7 is a partial vertical section view through a seventh embodimentof a reinforcing rod according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGS. 1 a) and 1 b), a reinforcing rod 1 is shown with twosuperimposed rib types. Here, the reinforcing rod 1 is made from acylindrical basic shape with circular cross section, starting from whichfirst recesses 2 and second recesses 3 extend inwardly in the radialdirection, by which overlapping ribs 4, 5 are formed. The recesses 2, 3are arranged running in opposite senses relative to each other, that is,one recess has a right-handed course and the other recess has aleft-handed course along the reinforcing rod in the shape of a threadaround this rod. The recesses 2 here have a deeper construction than therecesses 3. The recesses 2 leave ribs 4 therebetween (in fact, athread-shaped, peripheral, continuous rib 4). Correspondingly, therecesses 3 leave recesses 5 therebetween which partially also overlapwith the ribs 4 due to the mutual overlapping of the recesses.

In FIG. 1 b), the surface of the reinforcing rod according to theinvention can be seen from the vertical section with the rod diameter d₂in the region of the recess 2 and the rod diameter d₃ in the region ofthe recess 3. Also, two details A, B, which are shown in FIGS. 1 e) and1 f), clarify the different rib or recess shapes. Both recesses have thesame flank angle α and the same curvature radii R₁ in the transitionregion between the recess base 2 a, 3 a and rib flanks 2 b, 3 b. Onlythe rib depths t₂, t₃ and the recess widths b₂, b₃ are different justlike the rib pitches T₂, T₃ (see FIG. 1 a)).

Review of the horizontal section in FIGS. 1 c) and 1 d) shows that therecesses 2, 3 or ribs 4, 5 produce overall an inhomogeneous surface ofthe reinforcing rod 1, which is responsible for the result thatdifferent regions have different shear load-bearing capacities and thusoverall the load-bearing capacity of the reinforcing rod can beimproved.

FIGS. 2 a) and 2 b) show an alternative reinforcing rod 21 with recesses22, 23, which run in the same sense in the shape of a thread along thereinforcing rod 21 and have different slopes. Also in this way, ribswith different geometric properties can be produced, which havedifferent shear loads on the rib base.

In FIGS. 3 a) and 3 b), a reinforcing rod 31 is shown, in which ribswith different geometric properties are provided one within the other.While the rib pitch T₄, that is, the distance between adjacent threadsof the thread-shaped, peripheral rib is the same across the entirereinforcing rod, the depth t₄, t₅ of the recess 22, however, changesacross the axial length of the rod. In this way, ribs 24, 25 withdifferent geometric properties transition into each other continuouslyand without steps and have correspondingly different load-bearingcapacities due to the different rib depth t₄, t₅.

With reference to FIGS. 4 to 7, the system of the rib shapes can beclarified. For example, FIG. 4 shows a reinforcing rod 41 with a rib 42of first order and a recess 43 with a rib depth t₄₂, a flank inclinationangle α, a pitch T₄₂, which is the combination of the rib width B₄₂ plusthe distance b₄₂ between two adjacent ribs.

In FIG. 5, now for a reinforcing rod 51 of a rib corresponding to therib 42 of first order from FIG. 4 and also a recess corresponding to therecess 43 from FIG. 4, a narrower rib 52 of second order and alsonarrower recesses 53 are superimposed, which form together with the ribof first order an order system made from narrow ribs of higher order 52,54, 55, 56 and a wide rib 57 of lower order, which carries the narrowribs. It is not difficult to see that in a loaded case, the narrow ribsshear off more quickly and that, however, when they are sheared off, thewide rib 57 still creates a bond with the concrete surrounding thereinforcing rod and thus the rod 51 does not fail suddenly at the sametime in all anchoring sections.

FIG. 6 and FIG. 7 finally show for reinforcing rods 61, 71,multiple-step ribs 62, 72, which are likewise the result ofsuperimposing several ribs, wherein the rib sub-regions 62 a, 62 b, 62 chave different flank inclinations α₀, α₁, α₂ and different rib widthsB₀, B₁, B₂. In contrast, for the multiple-step rib 72 from FIG. 7, thetransition between the sub-regions of the rib is continuous withcontinuous changes in width and angle.

The multiple-step ribs also lead to the result that, if there is doubt,initially the narrowest sub-rib 62 c shears off earlier than the widestsub-rib 62 a and thus similarly provides for an improvement of theload-bearing capacity of the associated reinforcing rod 61.

In summary, the present invention offers the advantage through formationof ribs with different geometric and/or material properties to improvethe connection behavior of fiber-reinforced plastic reinforcing rods,whose application behavior in the load case is to be optimized and thussuch plastic reinforcing rods are to be opened up to additionalapplication possibilities. Consequently, a reinforcing rod made fromfiber-reinforced plastic is provided, which helps to reduce the crackspacing and the crack width in the concrete surrounding the reinforcingrod, which leads to the described advantages.

1. Reinforcing rod comprising fiber-reinforced plastic, provided on aperipheral surface thereof with profiling projecting outwardly in aradial direction as ribs extending at least across one part of theperipheral surface, the ribs (4, 5, 42, 52, 54, 55, 56, 57, 62, 72) withdifferent geometric and/or material properties.
 2. Reinforcing rodaccording to at least claim 1, wherein the ribs (4, 5, 42, 52, 54, 55,56, 57, 62, 72) with the different geometric and/or material propertiesare constructed such that, in a load case, they have a different shearload capacity on a rib base.
 3. Reinforcing rod according to at leastclaim 1, wherein the ribs (4, 5, 42, 52, 54, 55, 56, 57, 62, 72) withthe different geometric and/or material properties are constructed suchthat, in a load case, the ribs fail at different times and/or underdifferent loads.
 4. Reinforcing rod according to claim 1, wherein theribs (4, 5, 42, 52, 54, 55, 56, 57, 62, 72) with the different geometricand/or material properties are arranged at least in approximately a sameaxial section of the reinforcing rod adjacent to each other, borderingeach other, with mutual spacing, and/or mutually overlapping oneanother.
 5. Reinforcing rod according to claim 1, wherein the geometricand/or material properties of the ribs (4, 5, 42, 52, 54, 55, 56, 57,62, 72) are constructed in multiple steps across an axial length of thereinforcing rod (1, 21, 31, 41, 51, 61, 71) and/or a periphery thereof.6. Reinforcing rod according to claim 1, wherein the different geometricand/or material properties of the ribs (4, 5, 42, 52, 54, 55, 56, 57,62, 72) include rib height (t), rib spacing (b), rib pitch (T),inclination angle (α) of the rib flanks, slope of the ribs, and/or ribshape.
 7. Reinforcing rod according to claim 1, wherein the differentgeometric and/or material properties of the ribs include different fibercontent, different materials of the reinforcing rod and/or fibers and/ordifferent fiber orientations.
 8. Reinforcing rod according to claim 1,wherein the ribs (62 a, 62 b, 6 c) are combined into a multiple step rib(62) constructed one on the other in the radial direction, in whichseveral ribs with different geometric and/or material properties arearranged at least partially superimposed on each other or overlapping.